A drastic conformational change in the
trans-activation motif observed in the crystal structure of the disulfide
cross-linked Fis V13C mutant

Wei-Zeng Yang (楊維仁),
Li-Chu Tsai (蔡麗珠) and Hanna S. Yuan (袁小琀)

Institute of Molecular Biology,
Academia Sinica, Taipei, Taiwan, ROC.

中央研究院 分子生物研究所

Fis protein was first discovered by its critical role in
stimulating site-specific DNA inversions in enteric bacteria.Our previous X-ray crystal structure
analyses of wild-type and mutant Fis proteins reveal that Fis contains a
N-terminal mobile b-hairpin
arms where is the trans-activation region responsible for direct interactions
with invertases.In order to
better understand the structural and functional roles for the residues located
in this region, we have resolved the crystal structures of a series of Fis
N-terminal mutants, including V13C T15C, V16C, Q21C, D20K, H22V, and S18C/K36E.

In all these mutant structures, the disulfide cross-linked
V13C reveals an unexpected drastic conformational change in the trans-activation
region.V13C is active in the
reduced form and inactive in the oxidized form in the Hin catalyzed DNA
inversion reaction.The crystal
structure of the oxidized V13C, solved by molecular replacement methods, shows
that the two b-strands
in the b-hairpin
arms are detached resulting in a movement more than 15 Å for the Ca-atom at 13 position.This result suggests that a b-hairpin
structure is likely retained in inversion and demonstrates that the
trans-activation motif in Fis is highly flexible that it can adopt different
conformations.